Three-Dimensional Modeling of a Fin-Actuated Robotic Fish With Multimodal Swimming

Dynamical model is always an important factor in controller design for robots. Existing models of robotic fish typically incorporate only planar motion, rarely considering spatial motion. This paper formulates a complete three-dimensional (3-D) dynamic model for the robotic fish actuated by pectoral and caudal fins, in which the fluid forces mainly contain quasi-steady lift and drag, gravity and buoyancy, and waterjet strike force. The critical lift and drag of flapping fins are derived with an explicit 3-D angle of attack. Taking a bioinspired central pattern generator as the system actuation, our model can produce multimodal maneuvers, including forward/backward swimming, turning, and ascending/descending, as well as complicated motions, such as rolling and spiraling. Motions simulated in a 3-D environment are experimentally validated with a free-swimming robotic fish. Furthermore, systematic comparisons between simulations and experiments are conducted over a wide range of the control parameter space for beating frequency, amplitude, and offset. The overall results demonstrate the effectiveness and the versatility of the developed 3-D dynamic model in the prediction of the robot trajectory, velocity, and attitude.